There are to be 6 homes built on a new development site. They could
be semi-detached, detached or terraced houses. How many different
combinations of these can you find?

Strike it Out for Two

Age 5 to 11 Challenge Level:

Here's a game to play with a grown-up!

How do you play?
You'll need a grown-up to play with.
You'll also need a number line from 0 to 20, like the one above. You can find some of these here.

The grown-up chooses a number on the line and crosses it out.
They then choose a second number and cross that out too.
Finally, the grown-up circles the sum or difference of the two numbers and writes down the calculation.

For example, the grown-up's go could look like this:

You must start by crossing off the number that the grown-up has just circled.
You then choose another number to cross out, and then circle a third number which is the sum or difference of the two crossed-off numbers.
You also writes down their calculation.

For example, once you have had a turn, the game could look like this:

Play continues in this way with each player starting with the number that has just been circled.

For example, the grown-up could then have a turn which left the game looking like this:

The winner of the game is the player who stops their opponent from being able to go.

What is your strategy for winning?
Can you cross out all the numbers in one game? How do you know?
What is the biggest number of numbers you can cross out?

Notes for grown-ups
Strike it Out offers an engaging context in which to practise addition and subtraction, but it also requires some strategic thinking. It is easily adaptable and can be used co-operatively or competitively.

Easier version: try starting with a number line from 0 to 10 instead.Harder version: try using multiplication and division as well as addition and subtraction. Children could suggest different number lines that they could use: maybe longer number lines, or ones involving decimal or negative numbers.

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the
NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to
embed rich mathematical tasks into everyday classroom practice.